JP2012238647A - Optical element mounting package and optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element mounting package which, in a simple and inexpensive configuration, can prevent occurrence of multiple reflection due to impedance mismatch, thereby making it possible to reduce reflection losses.SOLUTION: The optical element mounting package comprises an LD 7, a PD 6 and a system 5 on which the LD 7 and the PD 6 are mounted. The optical element mounting package further includes a first lead pin 1 connected to the cathode electrode of the LD 7, a second lead pin 2 connected to the cathode electrode of the PD 6, a third lead pin 3 connected to the anode electrode of the LD 7, and a fourth lead pin 4 directly connected to the system 5. The first to fourth lead pins 1 to 4 are arranged in concentric circular form, where the first lead pin 1 and the third lead pin, and the second lead pin and the fourth lead pin, respectively, are disposed diagonally across the center of the concentric circle, the center distance between the first lead pin 1 and the third lead pin 3 being shorter than that between the second lead pin 2 and the fourth lead pin 4.

Description

  The present invention relates to an optical element mounting package for mounting an optical element such as a light emitting element or a light receiving element and performing high-speed communication, and an optical module including the package.

  Conventionally, in the field of optical communication, an optical element mounting package (also referred to as a CAN package) on which an optical element such as a light emitting element (LD: Laser Diode) or a light receiving element (PD: Photo Diode) is mounted is known. In such a CAN package, with an increase in demand for high-speed communication in recent years, transmission signals have been increased in frequency and transmission speed. However, when a signal having a higher frequency is transmitted, Even a slight impedance gap in the connection portion on the line has a problem that loss due to multiple reflections increases and transmission efficiency is lowered.

  To deal with the above problem, for example, Patent Document 1 describes an electronic component mounting package that can reduce reflection loss at the time of input / output of a high-frequency signal whose communication speed exceeds 6 Gbps. According to the technique described in Patent Document 1, the ceramic substrate 101 shown in FIG. 6 is attached to a wiring board on which an LD is mounted, or the relative dielectric constant of the glass sealing portion 102 shown in FIG. 7 is changed. Thus, the impedance on the signal line is matched.

JP 2010-62512 A

  However, in the method shown in FIG. 6, since it is necessary to attach the ceramic substrate to the wiring substrate by soldering or the like, the material cost of the ceramic substrate is increased and the manufacturing process of the ceramic substrate is increased, which increases the manufacturing cost. In addition, there is a problem that it is difficult to automate the mounting of the ceramic substrate. Further, in the method shown in FIG. 7, in order to obtain a desired impedance in the glass sealing portion, it is necessary to accurately seal the lead pin at the center of the through hole of the stem. There is a problem that it is difficult in practice and the impedance varies.

  The present invention has been made in view of the above-described circumstances, and for an optical element mounting that can reduce the reflection loss with a simple configuration without increasing the cost and preventing the occurrence of multiple reflections due to impedance mismatching. It is an object of the present invention to provide a package and an optical module including the package.

  An optical element mounting package according to the present invention includes a light emitting element that emits signal light from one end face, a light receiving element that receives leakage light emitted from a surface opposite to the one end face of the light emitting element, and the light emitting element and the light receiving element. A first lead pin connected to the cathode electrode of the light emitting element, and a second lead connected to either the anode electrode or the cathode electrode of the light receiving element. A lead pin, a third lead pin connected to the anode electrode of the light emitting element, and a fourth lead pin directly connected to the stem, wherein the first to fourth lead pins are concentrically arranged on the stem, 1 lead pin and 3rd lead pin are arranged diagonally across the center of the concentric circle, and 2nd lead pin and 4th lead pin are arranged diagonally across the center of the concentric circle Is the axial distance between the first lead pin and the third lead pin is shorter than the axial distance between the second lead pin and the fourth lead pin.

The cathode electrode of the light emitting element and the first lead pin are connected by a wire, and the anode electrode of the light emitting element and the third lead pin are connected by a wire, and the first lead pin of the first lead pin is connected from the cathode electrode through the wire. The cathode-side signal line length to the position where it intersects with the lower surface of the stem and the anode-side signal line length from the anode electrode to the position where it intersects with the lower surface of the stem of the third lead pin via the wire are converted into the wavelength of the signal speed emitted by the light emitting element. Desirably, it is less than ¼ of the value.
The light receiving surface of the light receiving element is preferably inclined with respect to the optical axis of the light emitting element.
An optical module according to the present invention includes the optical element mounting package described above.

  According to the present invention, the distance between the two lead pins connected to the LD is shortened, and the signal line length from the bottom of the stem to the LD is less than ¼ of the signal wavelength. Therefore, it is possible to reduce the distortion of the waveform of the transmitted optical signal by reducing the impedance mismatch points and preventing the occurrence of multiple reflections without incurring costs.

It is a figure which shows an example of the package for optical element mounting by this invention. It is the figure which showed typically the arrangement | positioning state of the 1st-4th lead pin in the package for optical element mounting of FIG. It is a figure which shows the XX cross section of FIG. It is a figure which shows an example of the state by which the cover part was united with the optical element mounting package shown in FIG. It is a figure which shows an example of the optical module provided with the optical element mounting package shown in FIG. It is a figure which shows the prior art of patent document 1. FIG. It is a figure which shows the prior art of patent document 1. FIG.

  FIG. 1 is a view showing an example of an optical element mounting package according to the present invention. 1A is a view when the optical element mounting package is viewed from above, FIG. 1B is a view when the optical element mounting package is viewed from the side, and FIG. 1C is an optical element mounting package. It is a figure when a package is seen from diagonally upward. FIG. 2 is a diagram schematically showing the arrangement of the first to fourth lead pins in the optical element mounting package of FIG. FIG. 3 is a view showing a XX cross section of FIG. In the figure, 1 is a first lead pin, 2 is a second lead pin, 3 is a third lead pin, 4 is a fourth lead pin, 5 is a stem, 6 is a light receiving element (PD: Photo Diode), and 7 is a light emitting element. (LD: Laser Diode), 8 is a heat sink, 8a is a submount on which a light emitting element is mounted, 9 is a submount on which a light receiving element is mounted, and 10 is an inclined recess.

  The optical element mounting package includes an LD 7 that emits signal light from one end surface, a PD 6 that receives leakage light emitted from a surface opposite to the one end surface of the LD 7, and a stem 5 on which the LD 7 and PD 6 are mounted. . The stem 5 is formed by pressing a metal plate such as iron (Fe), Kovar, SPC or the like into a disk shape and plated with Au. The inclined recess 10 (FIG. 3) and the heat sink 8 are integrally formed. The heat sink 8 protrudes in a semi-cylindrical shape on the upper surface portion of the stem 5, and the LD 7 is attached to the side surface via the submount 8 a and functions as a heat radiating plate for radiating the heat generated in the LD 7.

  As shown in FIG. 3, the inclined recess 10 has a bottom surface inclined at a predetermined angle, and the PD 6 is die-bonded to the inclined bottom surface via the submount 9 or directly without the submount 9. . In other words, the light receiving surface of the PD 6 is attached to be inclined with respect to the optical axis of the LD 7. This is to prevent the light emitted from the LD 7 from being reflected by the light receiving surface of the PD 6 to become return light. In the case of this example, the PD 6 is mounted on the upper surface portion of the stem 5 via the submount 9, but the bottom surface of the inclined recess 10 gradually becomes deeper in the direction from the fourth lead pin 4 to the second lead pin 2. Therefore, the light receiving surface of the PD 6 is inclined to the side opposite to the mounting surface of the LD 7 (in the direction of the second lead pin 2). Thereby, it can prevent more reliably that the reflected light in the light-receiving surface of PD6 returns to LD7.

  In FIG. 1A, the stem 5 is formed with three through holes, and the first lead pin 1, the second lead pin 2, and the third lead pin 3 are respectively formed in these three through holes with a low melting point glass. Is sealed with a sealing material (relative dielectric constant er) such as, and fixed to the stem 5. As a result, the sealing portions 1 a to 3 a are formed between the first to third lead pins 1 to 3 and the stem 5. The fourth lead pin 4 is directly fixed to the lower surface portion of the stem 5.

  Each component of the stem 5 and the first to third lead pins 1 to 3 is made of, for example, an iron-based alloy because electrical connection is required. Between the stem 5 and the first to third lead pins 1 to 3 is sealed with a glass material for hermetic sealing, but in order to prevent breakage of the hermetic sealing due to the difference in the linear expansion coefficient of the material It is necessary to select a suitable material. In the existing technology, there are a matched seal using a low linear expansion material such as Kovar, and a compression seal using a normal iron-based material such as SPC. Each metal part is plated with Au in order to eliminate the influence of oxidation or the like. By wire plating with Au, wire bondability is also improved.

  1B and 1C, the first lead pin 1 is connected to the cathode electrode of the LD 7 via a wire 7k. The second lead pin 2 is connected to a cathode electrode (or an anode electrode) of the PD 6 via a wire 6k. The third lead pin 3 is connected to the anode electrode of the LD 7 via a wire 7a. As shown in FIG. 1A, the first to fourth lead pins 1 to 4 are concentrically arranged on the stem 5, and the first lead pin 1 and the third lead pin 3 are centered on the concentric circle. The second lead pin 2 and the fourth lead pin 4 are arranged diagonally across the center of the concentric circle.

As shown in FIG. 2, the inter-axis distance m ₁₃ between the first lead pin 1 and the third lead pin 3 is shorter than the inter-axis distance m ₂₄ between the second lead pin 2 and the fourth lead pin 4. The That is, the first to fourth lead pins 1 to 4 are arranged in a diamond shape with diagonal lines passing through the center of the stem 5 when viewed from the upper surface of the optical element mounting package.

  In FIG. 1B, the cathode electrode of the LD 7 and the first lead pin 1 are connected by a wire 7k, and the anode electrode of the LD 7 and the third lead pin 3 are connected by a wire 7a. Then, the cathode side signal line length L1 from the cathode electrode of the LD 7 to the position intersecting the lower surface of the stem 5 of the first lead pin 1 through the wire 7k and the stem of the third lead pin 3 from the anode electrode of the LD 7 through the wire 7a. 5 The anode-side signal line length L2 up to the position where it intersects the lower surface is less than ¼ of the wavelength converted value of the signal speed emitted by the LD7.

That is, the relative permittivity of the sealing portion 1a is er, the length (stem thickness) of the sealing portion 1a is d ₀ , the length of the inner lead of the first lead pin 1 is d ₁ , and the wire from the inner lead to the LD 7 If the length of 7k was d _3, the cathode-side signal line length L1 is
_{L1 = d 0 × er + d} 1 + d 3 ... Formula (1)
When the above wavelength conversion value is λ,
λ / 4> L1 Formula (2)
The cathode side signal line length L1 is determined so as to satisfy the above condition.

Similarly, the relative permittivity of the sealing portion 3a is er, the length (stem thickness) of the sealing portion 3a is d ₀ , the length of the inner lead of the third lead pin 3 is d ₁ , and the length from the inner lead to the LD 7 If a length of up to the wire 7a was d _2, anode-side signal line length L2 is
_{L2 = d 0 × er + d} 1 + d 2 ... Equation (3)
When the wavelength conversion value is λ,
λ / 4> L2 Formula (4)
The anode-side signal line length L2 is determined so as to satisfy the above condition.

To meet the conditions of the aforementioned formula (2) and (4), it is necessary to shorten the first lead pin 1 and the center distance m ₁₃ of the third lead pin 3. For example, the relative dielectric constant er of the sealing portion is 4.1, the inter-axis distance m ₁₃ between the first lead pin 1 and the third lead pin 3 is 1.35 mm, the sealing portion length d ₀ is 1.0 mm, the inner lead length The _one having d ₁ of 0.9 mm, the LD7 chip width of about 0.25 mm, and the PD6 chip width of about 0.38 mm is used. The inter-axis distance m ₂₄ between the second lead pin 2 and the fourth lead pin 4 does not need to be as short as the inter-axis distance m ₁₃ between the first lead pin 1 and the third lead pin 3, and the PD 6 is mounted. What is necessary is just to set to the extent which does not have trouble in the binding process, such as a wire of LD7 or PD6, securing an area.

  In this way, the cathode-side signal line length L1 and the anode-side signal line length L2 can be handled as a lumped constant circuit by suppressing them to less than ¼ of the wavelength conversion value λ converted into the wavelength at the operating frequency. The lumped constant circuit generally refers to a circuit that is configured with an electronic component having a shape sufficiently smaller than the wavelength of the frequency or a sufficiently short wiring length, and is so small that the impedance of the wiring between the components can be ignored. As a concept of this lumped constant circuit, there is a distributed constant circuit. In designing a high frequency circuit, it is known that when a wiring length is basically λ / 4 or more, it is necessary to handle the wiring as a distributed constant line.

  Therefore, in this embodiment, the signal line length that becomes the boundary between the lumped constant circuit and the distributed constant circuit is λ / 4, and the cathode side signal line length L1 and the anode side signal line length L2 are suppressed to less than λ / 4. These signal lines are configured to be handled as a lumped constant circuit. Further, by limiting the signal line length to less than λ / 4, the impedance mismatch point becomes substantially one point, and multiple reflection does not occur, so that a good optical waveform can be obtained. In addition, a line of less than λ / 4 is not subject to design restrictions considering impedance matching.

  FIG. 4 is a diagram illustrating an example of a state in which a lid is combined with the optical element mounting package illustrated in FIG. 1. 4A is a side view and FIG. 4B is a bottom view. In the figure, 11 indicates a CAN package, and 12 indicates a lid. The lid 12 cooperates with the stem 5 to realize an optical element mounting space such as an LD or PD on the stem 5. Both the lid portion 12 and the stem 5 are made of metal, and both are combined while hermetically sealing the optical element mounting space by performing projection welding (also referred to as resistance welding) on the root portion of the lid portion 12 to the stem 5. The As described above, the optical element mounting package is configured as the CAN package 11 by combining the lid 12 with the stem 5.

  The lid portion 12 may be provided with a window portion that transmits light at a portion facing the LD 7. In this case, a hole is provided in a portion of the lid portion 12 facing the LD 7, and a window portion is integrally formed in this hole by joining or molding a flat plate or lens-shaped glass member with low melting point glass or the like. The metal material of the lid portion 12 preferably has a thermal expansion coefficient comparable to that of the flat plate-like or lens-like glass member.

  FIG. 5 is a diagram showing an example of an optical module including the optical element mounting package shown in FIG. In the figure, reference numeral 13 denotes an optical module. The optical module 13 of this example is configured by integrating the CAN package 11 of FIG. This optical module 13 is equipped with an optical element such as a PD or LD inside the CAN package 11 and has an alignment mechanism such as a condensing lens and a sleeve for optically coupling these optical elements to an optical fiber. Is. Thus, the present invention may be in the form of an optical module provided with an optical element mounting package.

  As described above, according to the present invention, the distance between the two lead pins connected to the LD is shortened, and the signal line length from the bottom of the stem to the LD is less than ¼ of the signal wavelength. With a simple structure, it is possible to reduce the distortion of the waveform of the transmitted optical signal by reducing impedance mismatch points and preventing the occurrence of multiple reflection without cost.

DESCRIPTION OF SYMBOLS 1 ... 1st lead pin, 1a-3a ... Sealing part, 2 ... 2nd lead pin, 3 ... 3rd lead pin, 4 ... 4th lead pin, 5 ... Stem, 6 ... PD, 7 ... LD, 6k, 7a, 7k ... wire, 8 ... heat sink, 8a, 9 ... submount, 10 ... inclined recess, 11 ... CAN package, 12 ... lid, 13 ... optical module.

Claims (4)

A light-emitting element that emits signal light from one end face; a light-receiving element that receives leakage light emitted from a surface opposite to the one end face of the light-emitting element; and a stem that mounts the light-emitting element and the light-receiving element. A package for mounting optical elements,
A first lead pin connected to the cathode electrode of the light emitting element; a second lead pin connected to either the anode electrode or the cathode electrode of the light receiving element; and a third lead pin connected to the anode electrode of the light emitting element. And a fourth lead pin directly connected to the stem,
The first to fourth lead pins are concentrically arranged on the stem, and the first lead pin and the third lead pin are arranged diagonally across the center of the concentric circle, and the second lead pin A lead pin and the fourth lead pin are arranged diagonally across the center of the concentric circle;
An optical element mounting package, wherein an inter-axis distance between the first lead pin and the third lead pin is shorter than an inter-axis distance between the second lead pin and the fourth lead pin.   The cathode electrode of the light emitting element and the first lead pin are connected by a wire, and the anode electrode of the light emitting element and the third lead pin are connected by a wire, and the first electrode is connected to the first lead pin through the wire. The cathode-side signal line length up to a position where one lead pin crosses the lower surface of the stem and the anode-side signal line length from the anode electrode to a position where it intersects the lower surface of the stem of the third lead pin via the wire, respectively, The optical element mounting package according to claim 1, wherein the optical element mounting package is less than ¼ of a wavelength converted value of a signal speed emitted from the element.   The optical element mounting package according to claim 1, wherein a light receiving surface of the light receiving element is inclined with respect to an optical axis of the light emitting element.   An optical module comprising the optical element mounting package according to claim 1.

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